The 3rd Generation Partnership Project (3GPP) defines specifications of the method and apparatus for implementing VCC in 3GPP Rel 7 (see TS 23.206 and TS 24.206), and supports seamless handover of mobile users between a Circuit Switched (CS) domain and a Packet Switched (PS) domain.
However, the specifications do not support the existing Intelligent Network (IN) users of the Global System for Mobile Communications (GSM)/Universal Mobile Telecommunications System (UMTS), and the VCC service is implemented for only non-IN users.
At the initial deployment of the IP Multimedia Subsystem (IMS), 2nd Generation (2G)/3rd Generation (3G) users in the existing network account for a large percentage, while new IMS users account for a small percentage. Therefore, if the existing GSM/UMTS IN users are not supported, the VCC service is hard to implement.
The 3GPP defines a reference model for implementing the VCC service in 3GPP TS 23.206. FIG. 1 shows a networking diagram of a VCC service system in the prior art. In FIG. 1, the Home Location Register (HLR) and the Home Subscriber Server (HSS) are set independently; in the actual deployment, an operator can integrate the HLR with the HSS according to the capabilities of devices.
During the implementation of the present invention, the inventor finds at least the following problems in the prior art:
For each mobile operator, the percentage of prepaid users is high (more than 70% or even more than 95% for some operators); the prepaid service and other IN services such as the Virtual Private Network (VPN) run on the Service Control Point (SCP), and the users of such services have subscribed to an IN service. In the foregoing solution, a user requesting the VCC service must subscribe to the VCC service, but the mobile IN protocol does not support subscribing to two IN services concurrently. Therefore, the solution implements the VCC service for only the mobile users who have not subscribed to the IN service. Because the percentage of the mobile users who have not subscribed to the IN service is small, the implementation of the VCC service is limited greatly.
The interface between the SCP and the VCC Application Server (AS) is added. If the SCP is used to implement the VCC service, the SCP software of the existing network needs to be upgraded, which will affect the IN service carried by the SCP of the existing network.
The interface between the SCP and the VCC AS is not defined, and interconnection between the VCC AS and the SCP of the existing network needs to be tested. When the VCC AS and the SCP are from different manufacturers, the interconnection may fail.